Micro Tunneling and Pipe Jacking System
An effective trenchless method for building tunnels with small diameters is micro tunnelling. The technique is beneficial for installing pipelines beneath trains, highways, and other sensitive regions with the least inconvenience to nearby companies and traffic. In different ground conditions, it delivers exact line and level installations. The main networks for micro tunnelling include sewage, drinking water, communications, and power.
Since it is not practical for an operator to operate the tunnelling machine due to the small diameter of these tunnels (about 500mm to 4,000mm in diameter), a remotely operated micro tunnel boring machine (MTBM) in conjunction with the pipe jack-and-bore method is used for construction. Pipe jacking involves inserting specially made jacking pipes from one shaft to another into a tunnel bore created by a shield or another method.
The following components make up a pipe jacking and micro tunnelling system:
It is a steerable, automated tiny boring machine with an appropriate cutter head at the front for digging tunnels with smaller diameters. It uses a laser guidance system to send the operator real-time feedback and a forecasted position. The machine is driven by the operator using a steering jack.
Automated System for Cleaning Up Spills
Discharge pumps move the slurry up to the vibrating screen, where the coarse material is screened out and dumped into a container, then via the circuit to the separation plant. Pumps are then used to move the screened suspension into cyclones, where the fine material is removed.
To advance the pipes and the shield through the ground, it consists of high-thrust hydraulic jacks installed on a jacking frame that can apply the necessary jacking force against a specially designed thrust wall.
It consists of a laser beam device mounted on the jacking shaft, with the beam’s level, gradient, and alignment adjusted. Some devices transform the laser part into digital data using photosensitive cells on the target panel, which is placed at the back of the shield.
A remote-control device
The shield and associated equipment are operated by the remote-control system. Important data is measured, monitored, and recorded, and any errors can be observed on the monitor.
Process for Microtunnelling Planning
Testing of the soil and rocks as well as the gathering and presentation of geotechnical data are all part of the microtunnelling planning phase. On the basis of this, the project’s MTBM system and slurry separation equipment are chosen. Below is a description of the steps:
Determine the position and grade of the pipeline: Knowledge of the ground’s characteristics and the equipment’s capabilities is necessary to determine the pipeline’s position. This can be done by looking at previous building projects and figuring out any obstacles in the way of the planned tunnel route. To reduce costs and prevent problems during construction, it is advisable to plan ahead for the length of individual drives and the placement of shafts.
Collection of data: For the project’s planning, bidding, and construction to be successful, the project owner should conduct an excessive number of borings, test pits, and laboratory experiments. Use test trenches or large-diameter bucket borings on sites containing stones and cobbles.
Laboratory testing: Standard index testing provides accurate results. Using hydrometers to analyse grain size will provide the clay percentage. This information can be used to determine screen sizes, the number of hydro cyclones, and whether a centrifuge system would likely be necessary.
Construction Using Microtunnels
The ideal micro tunnelling system should be chosen to excavate the ground with maximum productivity and the least amount of danger based on the outcomes of the planning process. The following steps can be used to categorise the construction process:
- Create the launching and reception shafts at the tunnelling drive’s opposing ends.
- To drive the MTBM into the soil, hydraulic jacks should be used in the launch shaft.
- Slurry water-filled pipes should be used to carry the excavated spoils to the surface.
- The slurry lines and control cables need to be removed, and the jacks need to be retracted.
- Between the jacking frame and the MTBM, a pipe or casing needs to be dropped into the shaft.
- Reconnecting the slurry lines and control cables is necessary before moving the MTBM to a different drive.
- Until the MTBM reaches the reception shaft, the procedure should be carried out again.
- The MTBM and accompanying machinery must be retrieved.